During the mid 1990s or so there were rumors of a “new” Zn carbonate at SH. The rumors also had it that the stuff looked something like what’s in the photo (click on the thread title at top).

It IS a carbonate – it dissolves completely with effervescence in HCl.

I don’t think it’s dypingite, which is, in any case, a Mg carbonate and was identified in 1979. If I remember correctly, dypingite forms “tracks”, is fluorescent and has a radial structure. This stuff doesn’t do any of that.

Anyone know what happened with the supposedly “new” Zn carbonate – or what this stuff might be?

It is, indeed, Dunn's "Mineral F". As he explained it to me long ago, he had the mineral described and characterized, and had submitted to the IMA for approval. However, he had some second thoughts about the complete characterization and decided to withdraw it. It would likely have been approved back then, as full structural work was not demanded at the time.

Several years later, John Cianciulli (then curator at the Franklin Mineral Museum) and I worked on the material from an optical and chemical standpoint, and we offered material to John Rakovan for description and eventual IMA submission. However, John was unable to carry it all the way through due to the minute size of the crystals we had. Today, it remains an unnamed phase, awaiting some researcher who is willing and able to tackle it anew.

Modris, you have hit the proverbial point of frustration. Until someone picks up the ID challenge it will remain this way. I think if you collect some of the more prolific mineral deposits (like Franklin,NJ and MSH) you will end up with a sub-collection of unknowns hoping for someone to illumin us further in their identidty.Steve.